JPS59160308A - Piezoelectric ceramic vibrator for mechanical filter and mechanical filter using it - Google Patents

Abstract

PURPOSE:To obtain a mechanical filter with oscillators which has superior stability and reliability and is manufactured easily by coupling plural oscillators each consisting of piezoelectric ceramic and a couple of metallic rod pieces joined to its top and reverse surfaces. CONSTITUTION:Metallic thin pieces 21a and 21'a in the same shape which are aligned to the center of the piezoelectric ceramic 11, made of constant-elasticity metallic materials, and adjusted so that the temperature coefficient of a complex oslcillator is zero are provided on the top and reverse surfaces of the piezoelectric ceramic 11a to length shorter than the overall length of the ceramic 11. Metallic thin pieces 21'a and 12'b of plural oscillators are coupled by couplers to constitute the mechanical filter. Thus, the mechanical filter which has superior stability and reliability, facilitates impedance adjustment, and suppresses the tertiary spurious mode easily is manufactured easily.

Description

[Detailed description of the invention] (1) Technical field of the invention The present invention relates to mechanical filters.

(2) Technical Background Filters play an important role in the transmission of signals or data. An example is PCM [plays an important role as a timing extraction filter in a transmission device.

Generally, LC filters, that is, electrical filters are mainstream as such filters. However, with the advancement of LSI in recent years, there has been a strong demand for smaller size, higher stability, and higher reliability of various parts, and the LC filters are no longer functional enough to meet these demands. ing. Therefore, there has been a growing trend to use mechanical filters in place of the more rigid T and C filters.

(3) Prior Art and Problems Mechanical filters usually consist of a plurality of vibrators, couplers, support wires, etc., and vibrating parts using piezoelectric materials are promising as the vibrators. In particular, timing extraction filters built into PCM home equipment, etc. have relatively low frequencies (approximately 20
0 kHz), and conventionally, mechanical filters (ceramic filters) using piezoelectric ceramic vibrators in longitudinal vibration mode have been mainly studied. However, although this type of ceramic filter has the advantage of being inexpensive, it has problems with stability against temperature and knee shock, and there is also a method of connecting the support wire that holds the piezoelectric ceramic vibrator directly to the electrode surface of the piezoelectric ceramic using solder, etc. Since this method can only be used in a variety of ways, problems such as electrode surface peeling may occur, which poses a problem in terms of component reliability. Furthermore, since the piezoelectric ceramic itself is a brittle material, it is necessary to be careful in handling it during manufacturing processes such as cutting and polishing.

(4) Purpose of the Invention In view of the above-mentioned conventional problems and drawbacks, it is an object of the present invention to provide a mechanical filter having a human search element that is excellent in stability and reliability and easy to manufacture. It is something.

(5) Structure of the Invention In order to achieve the above object, the present invention provides a mechanical filter comprising a plurality of vibrators, a coupler and a support wire connected between them, in which each of the plurality of vibrators has the following features: It is composed of a piezoelectric ceramic having a rectangular plate shape and polarized in a predetermined direction in advance, and a pair of metal thin pieces made of a constant elastic metal material and bonded as electrodes to the upper and lower surfaces of the piezoelectric ceramic, respectively. This is a feature of the entire system.

(6) Examples of the Invention The present invention will be explained below with reference to the drawings. In addition, here,
This will be explained using a longitudinal vibrator as an example.

FIG. 1 is a perspective view showing a conventional vertical vibrator of the type closest to the present invention as a vertical vibrator used in a mechanical filter. In this figure, 1o is a longitudinal vibrator which is based on υ piezoelectric ceramic 11.

The piezoelectric ceramic 11 is polarized in its thickness direction.

This polarization is shown as arrow A in the figure. Note that piezoelectric ceramics are generally used after being subjected to such polarization treatment. This is to generate linear distortion with respect to changes in the electric field.

This electric field is generated by applying an alternating current voltage to the metal thin films 12 and 12' (only the top side shown) formed on the top and bottom surfaces of the piezoelectric ceramic 11 as both electrodes. That is, the longitudinal vibrator shown in FIG. 1 utilizes the transverse effect of displacement in a direction perpendicular to the direction of the electric field.

This alternating voltage is applied through leads 13 and 13'. In this case, the lead wires 13, 13' are connected to the metal thin films 12, 12', respectively, by solder joints or the like.

FIG. 2 is a perspective view showing a longitudinal vibrator used in the mechanical filter of the present invention. Note that the same reference numbers or symbols are given to the same components throughout the drawings. As is clear from the figure, the vertical vibrator 20 used in the mechanical filter of the present invention corresponds to the vertical vibrator 10 shown in FIG. 1 with thin metal pieces 21 and 21' further provided on the upper and lower surfaces.

Since these act as electrodes, the lead wires 13 and 13'
are connected to parts of these metal foils 21 and 21', respectively, rather than to the metal thin films 12 and 12' in FIG.

Further, a connector and a support wire, which will be described later, are connected via these thin metal pieces 21 or 21'.

In the case of FIG. 1, the lead wires, connectors, and support wires are bonded to the metal thin films 12 and 12', which is disadvantageous mainly in terms of strength, and is difficult to manufacture as a longitudinal vibrator for a mechanical filter. It is also disadvantageous in terms of stability and reliability. However, according to the present invention, as shown in FIG. 2, all metal flakes (not metal thin films) are introduced, so the above-mentioned difficulties and disadvantages are eliminated. What should be noted is that these metal flakes do not just eliminate these difficulties and disadvantages, but also produce new effects, which will be described later.

The metal foils 21, 21' have the same shape.

In short, exactly the same thing is provided on the top and bottom surfaces of the piezoelectric ceramic 11. If these thin metal pieces 21° and 21' are not the same, vibrations purely in the longitudinal direction of the piezoelectric ceramic 11 cannot be obtained, and unnecessary bending vibrations will occur. Further, the metal flakes 21 and 21' are made of a constant elastic metal material. It is generally known that the frequency temperature coefficient of a constant modulus metal material can be controlled by appropriately changing the heat treatment temperature of the constant modulus metal. Using this technique, for example, if the frequency temperature coefficient of the piezoelectric ceramic has a positive value at A%, the heat treatment temperature is adjusted so that the temperature coefficient of the constant modulus metal material becomes negative, and the piezoelectric ceramic The frequency temperature coefficient of the composite vibrator made of a constant elastic metal plate can be made to be zero temperature coefficient. In the end, metal flake 2
1.21' and piezoelectric ceramic 11 enables temperature compensation. Furthermore, these metal flakes 21.
Each center of 21' is made to coincide with the center of piezoelectric ceramic 11. This is to prevent unnecessary bending vibrations from occurring. The total length of these thin metal pieces 21, 21' is also shorter than the total length of the piezoelectric ceramic. In this case, it is conceivable to make the total length of these thin metal pieces 21 and 21' match the total length of the piezoelectric ceramic (that is, to sandwich the piezoelectric ceramic between these thin metal pieces to form a sandwich structure), but in the present invention, We purposely created a difference in the total length of the two. This is because when these are configured as mechanical filters, they have the advantage of easy impedance adjustment and easy removal of third-order streaks (described later).
.

When an AC voltage is applied between the lead wires 13 and 13' of the longitudinal vibrator 20 (FIG. 2) configured as described above, the longitudinal vibrator 20 is excited under the first longitudinal mode of a predetermined frequency. be done. In fact, in addition to the first mode, higher odd-order modes are also excited. However, these excitations are streaky.

FIG. 3 is a graph showing the frequency response characteristics of the longitudinal vibrator 20 shown in FIG. 2, in which the horizontal axis shows the frequency f, and the vertical axis shows the attenuation amount Loan. In this figure, the response waveform is
L3 and L5 represent the first mode, third mode, and fifth mode of longitudinal vibration, respectively. In addition, the metal thin piece 21
．． 21' have the same shape and are arranged in the same manner, so that streaks other than the vertical odd-order mode do not appear.

FIG. 4 is a perspective view showing an embodiment of the mechanical filter of the present invention using the vertical vibrator 20 of FIG. 2. FIG. Two cases are shown as longitudinal oscillators for counting, and each is distinguished by the suffix a and b. 41 in this figure is a support line, which plays the role of mechanically supporting the vertical vibrators 20a and 20bi. Therefore, they are connected at the nodes of each longitudinal child. This node is located at the center of each of the metal flakes 21a' and 21b'. Further, 42 is a connector. Note that a plurality of connectors 42 may be provided as long as they connect the pair of thin metal pieces 21a' and 21b'. However, it is not allowed to connect the thin metal pieces 21a', 21b' with the connector 42 and then connect the thin metal pieces 21a, 21b with the connector. This is because the input and output are short-circuited. It is joined to the thin metal pieces 218' and 21b' at a position other than the node. "This coupler 42 is excited in a bending vibration mode. The signal input side of the mechanical filter 40 configured in this way is IN, and the filtered output is obtained from the output side OUT.

The mechanical filter 40 configured as shown in FIG. 4 produces the special effects described below. The first effect is that impedance adjustment is easy. With the recent trend toward LSI, the input impedance Zin and output impedance Zouj of this mechanical filter 40
It is often required to differentiate between O. Specifically, it is Zin (Zout).
This condition is based on a design requirement to suppress voltage attenuation in the mechanical filter 40 as small as possible when eight circuits are connected.

The reason for producing the above first effect will be explained. FIG. 5 is a sectional view of the vertical camera 20a shown in FIG.
A case where the piezoelectric ceramic Ila is cut in the length direction is shown. FIG. 6 is a sectional view of the longitudinal vibrator 20b shown in FIG. 4, and the direction of the cross section is the same as that in FIG. 5. Vertical vibrator 20a on the side related to input impedance Zin (Fig. 5)
and output impedance Z □vertical camera element 2 on the side related to ut
The difference from 0b (Fig. 6) lies in the presence or absence of the sleeve S. This slit S can be easily formed using a laser, for example. The conduction between the metal thin films on both sides of llS is cut off. When there is no slit S (Fig. 5), the total length of the electrode is Lp
If there is a slit S (FIG. 6), the total length of the electrode is TJM. Here, LP>LM, and the difference in length is related to the magnitude of zln and Zout.

Note that FIG. 7 is an equivalent circuit diagram common to the vertical vibrator 20a of FIG. 5 and the vertical vibrator 20b of FIG. 6. In this diagram, L
is an equivalent inductance component, C is an equivalent capacitance component, Cd is a damping capacitance, R is an equivalent resistance, and the resonance frequency fr is determined by the following. Note that fr in the case of FIG. 5 and fr in the case of FIG. 6 are the same. This is because the vibration frequency of a longitudinally vibrating piezoelectric ceramic depends only on its total length (the total lengths of the piezoelectric ceramics 11a and 11b are the same). Here, if the dimensions of the piezoelectric ceramic and the metal flake are constant,
Comparing the magnitude of the equivalent inductance (L) in Figures 5 and 6, the electrode area is larger in the case without the slit S in Figure 5, so the electrical-mechanical conversion efficiency is better and L is smaller. . That is, if the equivalent inductance without the slit S (determining Zin) is smaller than the equivalent inductance with the slit S (determining Zout k), the desired Zin (Zout) is established.

It should be noted that this is satisfied simply by the presence or absence of the slit S.

Next, a mechanical filter 4 configured as shown in FIG.
The second effect obtained by 0 will be described. This second effect is that the third-order sgelious mode can be easily suppressed. In conclusion, L in Figure 6
It is sufficient to select the relationship between P and LM as LM″= a Lp.Practically speaking, as a mechanical filter, it is sufficient to satisfy this relationship only for the longitudinal oscillator on the output side.As mentioned above, If we assume a sandwich structure in which a piezoelectric ceramic (the total length of each is the same) is sandwiched between thin metal pieces, the relationship between LM and LP can be expressed as LM x L
It is possible to set it to P.

FIG. 8 is a graph showing the frequency response characteristics of the mechanical filter 40 of FIG. 4 that satisfies LM≠a Lp, and its horizontal and vertical axes are the frequency f and the attenuation t LO8B' as in FIG. 3. l: Show. As shown in this graph,
The third-order spurious mode L3 is significantly suppressed. Furthermore, the fifth-order surgical mode L5 is also considerably suppressed in its function as a mechanical filter.

Figure 9 is a graph used to explain the reason why the third-order spurious mode is significantly suppressed.
b), X is the length at the intermediate position), and the vertical axis represents the strain appearing in the piezoelectric ceramic (lla, llb).

To begin with, piezoelectric ceramics convert mechanical strain into alternating current voltage, and utilize the fact that positive or negative charges are induced by this mechanical strain. Then,
Focusing only on the third-order excitation mode, the total amount of charges induced by strain on the + side (indicated by hatched region 91) and the total amount of charges induced by strain on the negative side (shown by hatched region 92. 93) cancel each other out, and the induced charge eventually becomes zero. The third-order excitation mode will not appear as a filter output. This is the reason why the third-order Sgelius mode is suppressed.

(7) As described in detail, the present invention is exceptional in that it has excellent stability and reliability, is easy to manufacture, is easy to adjust impedance, and can easily suppress the third-order spurious mode. A mechanical filter with the following effects is realized.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a conventional vertical vibrator of the type closest to the present invention as a vertical vibrator used in a mechanical filter, FIG. 2 is a perspective view showing a vertical vibrator used in the mechanical filter of the present invention, and FIG. The figure is a graph showing the frequency response characteristics of the vertical vibrator 200 shown in FIG. 2, and FIG. 4 is a perspective view showing an embodiment of the mechanical filter of the present invention using the vertical vibrator 20 shown in FIG. , FIG. 5 shows the longitudinal vibrator 2 shown in FIG.
0a, FIG. 6 is the longitudinal vibrator 20b shown in FIG.
, FIG. 7 is an equivalent circuit diagram common to the longitudinal vibrator 20a in FIG. 5 and the vertical vibrator 20b in FIG. 6, and FIG.
Mechanical filter 40 in Fig. 4 that satisfies Lp k
FIG. 9, a graph showing the zero frequency response characteristic, is a graph used to explain the reason why the third-order spurious mode is significantly suppressed. 11a, 11b...piezoelectric ceramic, 12a, 12a
'. 12b, 12b'...metal thin film, 20a,
20 b-・-/f: vibrator, 21 a +21a
't 21 b + 21b'...Metal thin piece, 41
...Support line, 42...Connector, S...Slit. Patent Applicant: Fujitsu Limited, Patent Application Agent, Patent Attorney: Roo Aomi, Patent Attorney: Kazuyuki Nishidate, Patent Attorney (1) Yukio Patent Attorney: Akira Yamaguchi, Figure 1, Figure 2, Figure 3, f-+ Figure 5 Z kan414/

Claims (1)

[Claims] 1. In a mechanical filter consisting of a plurality of oscillators and a coupler and a support wire connected between them, each of the plurality of oscillators is polarized in a predetermined direction. 1. A mechanical filter comprising: a piezoelectric ceramic; and a pair of thin metal pieces each made of a constant-modulus metal material and bonded to an upper surface and a lower surface of the piezoelectric ceramic, respectively. 2. The piezoelectric ceramic is polarized in advance in the thickness direction using a transverse effect, metal thin films are formed on the entire upper and lower surfaces of the piezoelectric ceramic, and the pair of metal thin pieces have the same shape, and The total length thereof is shorter than the total length of the piezoelectric ceramic, and the support wire is arranged so that its center coincides with the center of the piezoelectric ceramic, and the support wire is joined to one of the pair of thin metal pieces at the center position of the thin metal piece, and 2. The mechanical filter according to claim 1, wherein the connector is joined to one of the pair of metal thin pieces at a position other than the center position of the metal thin pieces, and is excited in a bending imaging mode. 3. The mechanical filter according to claim 2, wherein in at least one of the plurality of vibrators, the total length LM of each of the metal thin pieces satisfies the LM key L p with respect to the total lengths t and p of the piezoelectric ceramic. 4. The mechanical filter according to claim 2, wherein in at least one of the plurality of vibrators, a slit is provided in each of the metal thin films in parallel with each end face of each of the metal thin pieces.